Safety while working with spark plug wires

[m_mcdonald at marx.ENET.dec.com]

> On Thu, 30 Nov 1995 m_mcdonald at marx.enet.dec.com wrote:

>> At idle speeds, most modern ignition systems should produce a spark
>> that jumps an air gap of at least 3/8" and displays a solid blue
>> color.  Be careful doing this by removing a spark plug wire while
>> the engine is running because you could get zapped,

>						-could- get zapped?

> A GM HEI got me once working around my distributor machine. The tightness
> across my chest was angina, lasted a week, and I never spoke a word about
> it to my wife, Lynn.  Please don't mess around with this stuff.

>> [You could get zapped if]
>> you remove it [spark plug wire at the boot] with one bare hand and
>> brace yourself to a metal part of the car with the other hand.
>> Inexpensive variable air gaps, that connect the end of a spark plug
>> wire inside its boot to ground via the air gap, are available.


> Just put a spark plug at the end of the cable and lay the plug on a 
> grounded surface. And don't touch it. Please be careful.

>				--Carter

Simply laying the plug on a grounded surface isn't a safe enough way
to look for a spark between the center and side electrodes.

1.  The spark plug body to grounded metal connection is by gravity
    alone -- which could lead to high resistance and inaccurate
    readings.

2.  When the engine starts, the vibration could bounce the spark plug
    to hanging in free air.  Then, 40,000 volts would be looking for
    the nearest ground and could find it at any number of undesirable
    places such as fuel rails.

I recommend using a short wire with a pair of alligator clips to
connect the side electrode to a good ground *AND* to hold the spark
plug in a safe place.  Better yet, NAPA and other stores sell a special
spark plug with a wide center electrode/side electrode gap and an
alligator clip riveted to the shell of the plug.  This clip both
gives a good ground connection and holds the plug in place.  It costs
a very reasonable $7.00 or so.

Carter is absolutely right.  High voltage in modern ignition systems
(and even in my 1940 Ford with its 6-volt coil and breaker points)
is something to treat with a great deal of respect and planning.  It
is dangerous, especially when passing from one hand through the heart
to the other and grounded hand.

Other comments about high-voltage safety are always welcome.

Marll McDonald   KB1AGM
m_mcdonald at marx.enet.dec.com